= x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( )
% < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9
( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8
9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7
8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6
7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5
6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3
116
S SUBTRACTIONUBTRACTION
Most of us fi nd addition easier than subtraction. Subtraction, the
way most people are taught in school, is more diffi cult. It need not
be so. You will learn some strategies in this chapter that will make
subtraction easy.
First, you need to know the combinations of numbers that add to
You learned those when you learned the speed math method of
multiplication. You don’t have to think too hard; when you multiply
by 8, what number goes in the circle below? You don’t have to
calculate, you don’t have to subtract 8 from 10. You know a 2 goes
in the circle from so much practice. It is automatic.
If a class is asked to subtract 9 from 56, some students will use an
easy method and give an immediate answer. Because their method is
easy, they will be fast and unlikely to make a mistake. Th e students
who use a diffi cult method will take longer to solve the problem
and, because their method is diffi cult, they are more likely to make
a mistake. Remember my rule:
CChapter 12hapter 12
